Pathological tissue in hollow organs means here in particular tumors of the mucosa (mucous membrane) of the gastro-intestinal tract, taking into account a possible invasion into the submucosa located thereunder. Known methods by which means pathological mucosa can be ensnared under endoscopic control by means of instruments suitable for this purpose and removed or ectomised or resected by RF surgery are polypectomy as well as mucosectomy or mucosal resection. Polypectomy can be used when the pathological tissue protrudes from the normal mucosal level (generally called polyp) and can be ensnared with an instrument available for this purpose and thus can thus be removed by RF surgery. If a pathological mucosal area does not protrude sufficiently far from the adjoining mucosal level so that it can be ensnared with an available instrument, it can be raised out from the adjoining mucosal level (generally called pseudo-polyp), for example, by injecting normal saline solution into the submucosa located thereunder, sufficiently far that it can be ensnared like a polyp and removed. This method is called mucosectomy or mucosal resection. The common purpose of this method is the complete removal of pathological mucosa and the submucosa located thereunder. This purpose is achieved when the pathohistological examination of the removed tissue confirms that the criteria of a RO resection are satisfied, that is, the ectomy or resection has been made in healthy tissue outside the pathological tissue so that one can be sure that the entire pathological tissue has been removed.
RF surgical instruments available for this purpose, in particular for endoscopic polypectomy in the gastro-intestinal tract, are so-called polypectomy loops. Both the loop-shaped electrodes in general and also (pars pro toto) the complete RF surgical instruments including the loop-shaped electrodes are designated by “polypectomy loop”. Since these instruments are not only suitable for the ectomy of polyps but also for the ectomy of other pathological tissue, for example, for the ectomy of a major duodenal papilla (papillectomy), for the ectomy or resection of pathological mucosal areas (mucosectomy or mucosal resection) etc., hereinafter the loop-shaped electrodes per se and where generally valid are called “loop” for short, the entire instruments including loop, where generally valid is called “instrument” for short, the polyps, papillae, pathological mucosal areas etc., where generally valid are called “target tissue” for short and the ectomisation or resection etc., where generally valid is called “removal” for short (removal includes cutting and coagulating or thermal haemostasis).
As shown schematically in FIG. 6, known instruments substantially include a loop 102, a flexible catheter 106, at least one flexible but sufficiently stiff manipulation wire 107 which is used inside the catheter for pushing out and pulling in the loop in the axial direction from or into the distal end 108 of the catheter 106 and for conducting the RF current required for the RF surgical removal of target tissue, and a handle 109 at the proximal end of the catheter which consists of a slide rail 110 and a slider 111 for the manual pushing out or pulling in of the loops from or into the distal end of the catheter. At least one electrical contact for the connection of an RF surgical generator (RF generator) is disposed on the slider. Bipolar loops are, for example, separated at their distal end 112 into two electrically separated loop sections and are mechanically interconnected by means of an electrically insulating connecting element 113.
With regard to the application of the RF current, a distinction is made between so-called monopolar methods and loops suitable for this, e.g. DE 2132808 and so-called bipolar methods and loops suitable for this, e.g. DE 102007008272 or DE 3220940.
Monopolar loops are characterized in that their RF-surgically effective sections can only be connected to one pole of an RF generator whilst the other pole of the RF generator must be connected to the patient via a neutral electrode. The RF current flows between loop and neutral electrode through the patient, i.e. not only through the target tissue but also through other tissue or tissue collateral to the target tissue. Monopolar loops exist today in various forms, with these however having no intentional influence on the RF surgical effects during the removal of target tissue but are intended to be used for mechanical manipulation or application according to the various localizations, sizes and/or shapes of the target tissue.
For more than 30 years ago now, it has been pointed out that when using monopolar loops, thermal damage to collateral tissue can be caused by the RF current flowing uncontrolledly between loop and the neutral electrode required in the monopolar method. Solutions to obviate this problem have been sought for just as long and again and again bipolar loops have been suggested as the solution in this respect.
Bipolar loops are characterized in that the loop, as for example that according to DE-G 7418576, is divided into two equal-length and mirror-symmetrically shaped loop sections (generally called symmetrical bipolar loop) or, as for example, that according to DE 3220940, into two different-length and generally asymmetrically shaped loop sections (generally called asymmetric bipolar or quasi-bipolar loops) and these loop sections are mechanically interconnected at their distal end by means of an element which electrically insulates the loop sections from one another. One of the two loop sections is connected to one pole and the other loop section is connected to the other pole of an RF generator. In this bipolar operating mode the RF current predominantly flows between the two loop sections through the tissue located between these loop sections. In symmetrical bipolar loops both loop sections should act as active electrodes. In asymmetric bipolar loops the shorter loop section should act as an active electrode and the longer loop section as a neutral electrode. A separate neutral electrode is consequently not necessary to operate a symmetrical or asymmetric bipolar loop. Accordingly, bipolar loops are connected to both poles of an RF generator so that the automatic monitoring of the connection of a neutral electrode to the RF generator prescribed in RF generators for monopolar operation and their application to the patient is not necessary or is disabled.
Bipolar loops or the bipolar operation of so-called bipolar loops has not, however, proved successful in clinical application. One reason for this is the electrical insulation sections at the proximal and at the distal end between the two loops sections. For RF surgical cutting the amplitude of the RF voltage between an active electrode used for cutting and the tissue to be cut must reach at least 200 Volts. Since in bipolar instruments at least 200 Volts having opposite polarity or phasing must be achieved simultaneously at each of the two active electrodes, the electrical insulation sections between the two active electrodes in particular at the proximal and at the distal end of the loop, where the distances between the two electrodes are very short, must withstand a voltage amplitude or amplitude difference of at least 400 V. If electrical arcs are formed between the two electrodes at these points, these electrodes can then melt as a result of the high temperature of these electrical arcs. According to DE 2514501, this problem should be solved by partial electrical insulation of the two loop sections which, however is not achieved or cannot be achieved at the distal end of the bipolar loop shown there.
Since the introduction of endoscopic polypectomy and mucosectomy, endoscopists would like to remove increasingly larger polyps or pathological mucosal/submucosal areas, in particular in the gastro-intestinal tract, for diagnostic and/or therapeutic purposes and this with a view to the pathohistological examination as far as possible in toto and as radically as possible to avoid recurrences. Radically means here including the submucosa of the affected mucosal area to as close as possible to the muscularis propria. As the size of the polyps ectomised in toto and radically or resected mucosal/submucosal area increases, however, when using hitherto available polypectomy or mucosectomy loops, the resulting complications and problems, especially bleeding and perforations also increase. In addition, only polyps or mucosal/submucosal areas up to about 2 mm diameter can be removed in toto with this method and the polypectomy or mucosectomy loops hitherto available for this purpose and the RF generators available for this purpose. Larger polyps or mucosal/submucosal areas can only be removed by this method in several smaller portions, the so-called piecemeal technique, and frequently are not removed radically or completely, which makes the pathohistological examination of the tissue thus removed and the allocation of a positive pathological finding to the respective resection site difficult or even impossible. In addition, tumors not removed completely can grow further.
Although polypectomy and mucosectomy are considered to be clinically established methods for the prophylaxis of malignant and especially metastasizing tumors, apart from the complications already specified above, these methods are beset with problems which also correlate with the size of the target tissue.
One of these problems, especially in the case of large polyps and/or sessile (flat growing) polyps as well as mucosal/submucosal areas which become large or even larger than they already are due to submucosal injection, are the electrical power or RF voltage and RF current required for their removal in toto. Since the RF surgical cutting effect can only occur when a vapor layer is present between the loop used for the cutting and the tissue to be cut, so that electric arcs are formed at sufficiently high RF voltages which burn away (pyrolysis effect) the tissue located near the loop, the tissue near the loop must be heated to the boiling point of water. If the heating of this tissue takes place too slowly and the cutting effect is consequently time-delayed (first cut delay), during the first cut delay the heat can diffuse from the near-loop tissue into adjacent tissue and damage this thermally. Thermal damage to the muscularis propria or even the serous membrane of an organ of the gastro-intestinal tract usually results in a perforation of the organ wall.
An RF current of at least 0.5 Ampere per cm of loop length is required for a sufficiently delay-free first cut in polypectomy or mucosal resection. Since RF generators of known RF surgical devices generate a maximum of 1.5 to 3 Amperes, only polyps having a diameter in the application range of the loop of about 1 to 2 cm, which corresponds to a loop length of about 3 to 6 cm, can be removed in toto with a sufficiently small first cut delay. In the case of larger polyps, the cutting effect is completely absent.
In order to reduce the RF current required for cutting and therefore to avoid a first-cut delay, it is proposed in DE 100 28 413 A1 to delimit the effective electrode surface of a monopolar loop electrode of the known type to a partial area in the vicinity of the electrode tip by means of an insulating sheathing of the two loop sections. The teaching according to DE 100 28 413 A1 substantially consists in concentrating, by means of a constructive measure, the effective electrode surface of the loop element only onto that surface region of the loop electrode on which the thermal cutting process of the loop electrode produced by the electrosurgical current flow should ideally take place. This constructive delimitation of the effective electrode surface by means of an at least partial insulation of the two loop sections should allegedly substantially simplify the handling of the electrosurgical instrument since the risk of miscuts or undesired contacts with healthy neighboring tissue is reduced to a minimum. The latter, however, only applies when the partial areas in the vicinity of the electrode tip are insulated partially on their circumference and/or at their tip, as is described for example in this DE 100 28 413 A1, which however can be disturbing or even obstructive during cutting guidance. A substantial disadvantage of the partial insulation of the circumference from partial areas of the loop, however, is the low efficiency of the coagulation or the thermal haemostasis.
DE 25 14 501 describes a bipolar coagulation instrument for endoscopes for the removal of polyps, for example, in the stomach, where a high-frequency current for haemostasis is fed to the electrodes and which is characterized in that the two electrodes form a loop whereby they are interconnected at their ends by means of an insulation piece. One embodiment of this coagulation instrument is characterized in that the electrodes are provided with an insulating layer over their entire length with the exception of an area in the vicinity of the insulation piece. When applying such a bipolar coagulation instrument, there should certainly be no first-cut delay but insulation problems in the area of the insulation piece when polyps are to be cut away by RF surgery using this coagulation instrument, for which RF voltages having amplitudes of at least 400 V are required. For coagulation or haemostasis, the partial insulation of the electrode on the circumference of the ends of the electrodes is rather disadvantageous because the effective contact areas are very narrow as a result.
U.S. Pat. No. 5,078,716 describes a monopolar polypectomy loop whose two loop sections are electrically insulated proximally apart from relatively short sections at their distal ends so that only a relatively short section at the distal end of the loop is uninsulated and thereby RF surgically effective. Such loops certainly require less RF current than equal-sized loops without insulation but have the disadvantage that the surgically effective part of the loop from the perspective of an endoscope is always behind the polyp, that is out of visual control, and there is the risk that in particular the distal tip of the loop can uncontrollably perforate especially thin-walled organs. Among other things, the subject matter of DE 100 28 413 A1 is to avoid the latter.
Both in electrosurgical instruments according to U.S. Pat. No. 5,078,716, DE 100 28 413 A1 and also in coagulation instruments according to DE 25 14 501, the RF surgically effective electrode surfaces are only disposed at the distal end of the loop with the disadvantage that these are always behind the tissue to be removed from the viewing direction of an endoscope and consequently become active without visual control.
A further problem is that large target tissue cannot be removed in toto but only in several smaller portions (piecemeal technique) from an organ wall using hitherto available loops and RF generators. At the present time various endoscopic submucosal dissection (ESD) methods are being developed for the in toto removal of larger mucosal/submucosal areas and some are already being used clinically. A common feature of these ESD methods is the RF surgical preparation of the relevant mucosal/submucosal area near the muscularis propria, for example, using a needle electrode. These methods require a high manual dexterity, experience, continuous training, willingness to take risks and a large amount of time. So far there are only a few experts practicing these methods.
To sum up, it can be noted with regard to the prior art here that many differently designed loops are now available or have at least been proposed for the endoscopic removal of target tissue (see above) but so far none is suitable for removing sufficiently reliably larger target tissue in toto, in particular larger than 2 cm in diameter.